1. Field of the Invention
The present invention relates to a method and device for inspecting for surface defects, internal defects, and surface-adhered foreign matter on semitransparent materials. Specifically, the present invention relates to a method and device for inspecting for surface defects, internal defects, and surface-adhered foreign matter on semitransparent hard disk substrates, liquid crystal display panels, lenses and the like.
2. Description of the Related Art
In general, inspection methods and inspection devices for detecting surface defects (scratches, pits), internal defects (air bubbles, contaminants), surface-adhered foreign matter (adhered small particles) (hereinafter referred to collectively as "defects") and the like in hard disk substrates, liquid crystal display panels, lenses and the like formed of semitransparent material can be separated into: inspection methods and inspection devices of the reflection type, which inspect for defects from information included in light reflected by the surface of the object being inspected (hereinafter referred to as "inspection object"); and inspection methods and inspection devices of the transmission type, which inspect for defects from information included in light transmitted through the inspection object.
In inspection methods and inspection devices of the reflection type, disadvantages arise in that the inadequate contrast between the scattered light from a defect area and the reflected light from the non-defect area due to low light reflectivity of the transparent or semitransparent inspection object prevents satisfactory defect inspection from being attained. Furthermore, the reflected light from the inspection object includes not only reflected light from the surface of the inspection object on the light source side (surface reflected light), but also includes reflected light from the surface of the inspection object on the side opposite the light source (back surface reflected light), which presents the disadvantage of eliminating the effects of this back surface reflected light from the inspection results.
In inspection methods and inspection devices of the transmission-type, on the other hand, while they do not have the disadvantages typical of the inspection methods and devices of the reflection type, they are subject to dispersion of the scattered light in all directions because they use a construction which condenses (collects) the light from a light source at the inspection position of the inspection object, i.e., they use a construction which causes light to enter the inspection position from various angles. This type of construction is disadvantageous in that there is insufficient contrast between the scattered light from a defect area and the transmitted light from the non-defect area, such that defect inspection cannot be readily accomplished.